Reduced losses in fibers, increased bandwidth, and mode locking of solid state laser sources in recent years have set the stage for optical communication links whose bit rates are much improved over contemporary usage. To date, however, all the signal handling has been done in the conventional electronic manner. Nevertheless, there has been a renewed interest in all-optical amplifiers, switches and signal processing to circumvent some of the conventional electronics problems for high speed operation. Several approaches have been explored: optical bistable devices, nonlinear Fabry-Perot (FP) resonators, nonlinear waveguide interferometers, nonlinear birefringent fibers, saturable gain media or Brillouin amplification, to note a few. Obviously, for optical signals in a fiber an all-optical processing device has a natural advantage provided its performance and compexity is on par with or better than, its electronic counterpart. On the other hand the theoretical bandwidth and speed advantages possible with all-optical devices are orders of magnitudes higher than electronic circuits. U.S. Pat. No. 4,505,301 Apr. 29, 1986 (Bialkowski) also teaches optically actuated optical switch apparatus and method. The patent uses a switching medium whose refractive index is changed by a control beam, selectively directed into the switching medium. The control beam produces a thermal gradient in the switching medium which in turn generates a refractive index gradient to produce a deflection of the probe beam.
Contrary to the above mentioned techniques, the present invention requires no Fabry-Perot resonators, feedback or strict wavelength control for any of the input/output beams. Therefore the device operation is noncritical and stable. Unlike the above-referenced patent, a very small power is required at the control to modulate a signal beam. Since, it is the extreme sensitivity of the fiber to fiber coupling to the effective numerical aperture ratio (mode overlap) that is used to provide the basic modulation technique instead of a simple deflection, the result is a drastic lowering in required energy to activate the modulator.